1. Field of the Invention
This invention relates to a temperature-controlled laser apparatus comprising a laser tube. This invention particularly relates to an external mirror type temperature-controlled laser apparatus.
2. Description of the Prior Art
Laser apparatuses comprising a laser tube are widely used in measuring instruments, analyzers, communication apparatuses, image read-out apparatuses, holographic apparatuses, welding apparatuses, medical apparatuses such as laser scalpels, nuclear fusion apparatuses, and the like.
One known type of laser apparatuses is the gas laser apparatuses. As gas laser apparatuses, there have heretofore been used external mirror type laser apparatuses wherein a pair of external mirrors for oscillating a laser beam are positioned independently from a cylindrical laser tube in the axial direction of the laser tube.
In the external mirror type laser apparatus, the external mirrors and mounts for supporting the laser tube for emitting a laser beam are installed on the same supporting plate. In this configuration, when a voltage is applied to the laser tube to cause it to emit a laser beam, much heat is generated by the center portion of the laser tube. The heat generated by the center portion of the laser tube is transmitted to the supporting plate via the mounts of the laser tube and by heat convection and heat radiation. Since the center portion of the laser tube generates the most heat, a difference in temperature arises between the center portion of the supporting plate above which the center portion of the laser tube is positioned and the peripheral portions of the supporting plate on which the external mirrors are positioned. In this case, among the mounts, the temperature of the mount supporting the center portion of the laser tube becomes the highest, and the temperatures of the mounts supporting the end portions of the laser tube become the lowest. As a result, in the supporting plate, a change in the temperature gradient arises such that the temperature of the portion of the supporting plate contacted with the mount supporting the center portion of the laser tube is higher than those of the portions of the supporting plate contacted with the mounts supporting the end portions of the laser tube. When this change in the temperature gradient arises in the supporting plate, the external mirrors are made to deviate in position with respect to the axial direction of the laser tube due to a difference in thermal expansion of the supporting plate. As a result, the intensity of the laser beam generated by the laser apparatus becomes low and, in the worst case, laser oscillation is not achieved. In order to eliminate this problem, adjustments of the positions of the external mirrors have heretofore been conducted periodically, for example, monthly. However, it is very troublesome to correct the positions of the external mirrors. Also, this method is not a one which prevents the external mirrors from deviating in position due to change in the temperature gradient arising in the supporting plate during the use of the laser apparatus.